Neurotransmission

Neurotransmission usually requires the release of endogenous chemicals, 'neurotransmitters', at synapses between neighbouring neurons. Neurotransmitters are synthesized and stored in the axons of neurons and release upon an increase of intracellular Ca²⁺, caused by an action potential. This releases neurotransmitters into the synapse where they can exert effects at postsynaptic neurons. They do this by binding to receptors (usually ligand-gated ion channels or GPCRs) and exerting an effect by causing ion influxes which depolarize the post-synaptic membrane, or by initiating a complex signaling cascade. Both these effects initiate an action potential at the postsynaptic neuron, propagating waves of energy downstream. Synaptic signals and action potentials are integral for all the information processing capabilities of the brain.

Neurotransmission and the strength of a connection between neurons can depend on a variety of factors. This includes; the number of synaptic contacts between 2 neurons, the size of post-synaptic depolarization elicited by neurotransmitters and the probability of neurotransmitter release. Many neurological diseases can occur due to defective flow of neurotransmitters at neuronal synapses. This may result in no impulse reaching the post-synaptic neuron and therefore no responses are exerted by the neurotransmitter downstream. Some examples of diseases with altered neurotransmission include; schizophrenia, depression, ADHD, anxiety disorder and Alzheimer's. Changes in neurotransmission have also been related to drug addiction.